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. 2025 Sep 22;9:txaf130. doi: 10.1093/tas/txaf130

Age at first mating and season of dam birth affect reproductive and productive traits of Mozambican Angoni cattle

Abilio Paulo Changule 1,✉, Leonel António Joaquim 2, Milton Paulo Morrombe 3, Hermenegilda Petersburgo Dias 4, Tiago Pereira Guimarães 5, Manuel Garcia-Herreros 6,7, Custódio Gabriel Bila 8,9,10,11
PMCID: PMC12973271  PMID: 41815891

Abstract

This retrospective observational study aimed to evaluate the effects of age at first mating (AFM) and season of dam birth (SB) on age at first calving (AFC), birth weight of calves (BW), and calving interval (CI) in Angoni cattle in Mozambique. A total of 1418 records collected over a 25-year period (1995–2020) at the Angonia Research Station were analyzed using R software (version 4.3.2). The effects of AFM and SB on reproductive and productive traits were determined using the Kruskal-Wallis test and further analyzed with Dunn’s test to compare means between groups in case of showing significance. The least squares method was applied to assess the relationship among AFM, BW, and AFC through simple linear regression analysis. AFM significantly influenced BW (17.5–18.3 kg; P < 0.05), AFC (839–1431 days; P < 0.001), and CI (493–533 days; P < 0.05). SB significantly affected BW (17.5 vs. 18.2 kg; P = 0.025) and CI (502 vs. 521 days; P < 0.001), but not AFC (P > 0.05). These results highlight that both AFM and SB are critical factors influencing reproductive performance and should be considered in future breeding and selection strategies to optimize herd efficiency in tropical beef systems.

Keywords: Age of first mating, Angoni breed, Mozambique, Reproductive traits, Season of dam birth

Age at first mating and season of birth significantly influenced reproductive performance in Angoni cattle, offering critical insights for improving breeding strategies in tropical systems.

Graphical abstract

Graphical Abstract.

Graphical Abstract

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Introduction

Reproductive efficiency is a critical factor in the sustainability and profitability of beef cattle systems, alongside genetics, nutrition, and animal health (Harvey Sky et al. 2024; Hindman et al. 2022; Michi et al. 2016; Rezende et al. 2020). In many production systems, suboptimal fertility extends calving intervals, increases involuntary culling, and raises input costs (Fernandez-Novo et al. 2020). Reproductive traits such as age at first conception, age at first calving (AFC), and calving interval (CI) are key indicators of herd productivity (Warburton et al. 2020).

In Mozambique, despite favourable agroecological conditions, beef production remains inefficient, characterized by low reproductive performance and a heavy reliance on imports to meet domestic demand (Aleixo 2023; Capaina 2020). Extensive systems dominate the sector, often lacking systematic control over breeding and reproductive cycles, leading to delayed puberty, late first calving (often ≥40 months in Bos indicus), and prolonged inter-calving periods (Burns et al. 2010; Cumbe 2023). These inefficiencies contribute to reduced numbers of weaned calves, increased age at slaughter, and lower meat quality, reinforcing consumer preference for imported beef.

Similar reproductive constraints have been reported in other tropical production systems relying on Bos indicus cattle. In Brazil, Nelore cattle, one of the most widely used zebu breeds often exhibit delayed puberty and extended AFC, which limit herd productivity under pasture-based systems (Perry 2016; Turiello et al. 2020). In India, Gir and Sahiwal cattle also display long calving intervals and high variability in reproductive traits, especially under extensive conditions with seasonal feed availability (López-Paredes et al. 2018). Likewise, studies in West African zebu breeds, including White Fulani and Gudali, highlight late maturity and prolonged calving intervals as major constraints for sustainable beef production (Maule 1973; Ng’Ang et al. 2018). Collectively, this evidence shows that reproductive inefficiencies are a common challenge for zebu cattle across tropical regions, reinforcing the need for breed-specific evaluations.

Angoni cattle, a Bos indicus breed adapted to tropical conditions and local forage resources, play a vital role in rural livelihoods in Mozambique (King et al. 2021; Maciel et al. 2016). Despite its resilience and multipurpose utility, little is known about its reproductive performance under field conditions. Historical reports suggest a downward trend in adult body weight over recent decades, highlighting potential concerns in herd productivity (King et al. 2022; Otto et al. 2000). To support more efficient use of this breed, understanding the factors that influence reproductive traits is essential. Rather than evaluating active management interventions, this study uses long-term archival data to explore natural variations.

Understanding how early-life factors influence reproductive outcomes is therefore essential. Evidence from Brazil, India, and West Africa suggests that both age at first mating (AFM) and season of dam birth (SB) can determine lifetime productivity in zebu cattle. AFM is closely linked to body development and nutritional status at puberty, while SB reflects environmental and seasonal effects that may have long-term consequences on female fertility and offspring growth (Bitencourt et al. 2020; Rezende et al. 2020). Given these parallels, we hypothesize that AFM and SB also influence key reproductive traits namely birth weight (BW), age at first calving (AFC), and calving interval (CI) in Angoni cattle in Mozambique. Accordingly, the objective of this study was to evaluate the influence of AFM and SB on BW, AFC, and CI in Angoni cattle raised under extensive tropical systems in Mozambique.

Materials and methods

Ethical approval

The requirement of ethical approval for the studies involving animals was waived by Faculty of Veterinary Medicine—Eduardo Mondlane University because ethical review and approval were not required for the study because only previous data records were used from the research database and none of the animals were handled or restricted at any time for this study. Therefore, the studies were conducted in accordance with the local legislation and institutional requirements.

Study area and climate conditions

Data for this study were collected at the Angonia Research Station (EZA) of the Zonal Center of the Agricultural Research Institute of Mozambique (Figure 1). EZA is in the district of Angónia (14°38′43′′S, 34°14′38′′E; Altitude: > 1000 m.a.s.l.), Tete Province, in the central-western region of Mozambique. The area is characterized by a tropical-humid climate (Köppen climate classification: BSw), with average annual temperatures ranging from 18 °C to 22 °C, relative humidity of 70%, and average monthly precipitation of 265 mm (Setâ et al. 2022). The rainy season typically occurs between November and April, while the dry season spans from May to October. The predominant cattle breed in the area is the Angoni, with a total population of approximately 33,864 individuals (Cumbe 2023). The annual average precipitation ranges between 1100 and 1200 mm, most falling between December and February. The soil in the region is deep and both flat or gently undulating, and agriculture is the main economic activity for the local population (Cumbula and Taela 2020).

Fig. 1.

Fig. 1.

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Location and climate of the Angónia research station, Mozambique. Study area location in the tropical-humid region of Mozambique (continent, country, province, district, and area) where data collection was performed including seasonal data and reproductive and productive performance in Mozambican Angoni cattle raised under tropical conditions. Continent: Africa; Country: Mozambique; Province: Tete; District: Angónia; Area: Ulongué. Tropical-humid study area (annual seasons: rainy and dry) located in Angonia Research Station (EZA) (white star).

Animal management

The livestock production system in this area has been characterized by using communal pasture areas, where animals from different farmers graze together. In these systems, cattle are kept in pens overnight and taken to pasture areas each morning, returning to their respective pens at the end of the day. The feeding system at the Angonia Research Station (EZA) is based on natural pasture, where animals graze for 8 hours daily. During the dry season (May to September), animals are strategically supplemented with Hyparrhenia rufa hay, leucaena leaves (Leucaena leucocephala), mulberry leaves (Morus alba), and locally produced mineral blocks. Calves are weaned at 6–8 mo. when they reach 30%–40% of their adult weight. The animals are dewormed annually at the beginning and end of the rainy season. Acaricide treatments using regular baths are administered whenever infestation levels are high, with increased frequency during the rainy season. Also, the animals are immunized against several notifiable diseases in Mozambique, including anthrax, foot-and-mouth disease, brucellosis, tuberculosis, and lumpy skin disease. The bulls and cows were kept together throughout the year allowing them to breed and calve continuously.

Experimental design

Retrospective data on ages at first calving (AFC) of dams, birth weights (BW) of calves, and calving intervals (CI) were extracted from record sheets spanning 1995 to 2020 (Joaquim et al. 2024). Animals with incomplete data or those that had not completed their first calving by the time of data collection were not selected for the study. Age at first mating was estimated based on the age at birth, and birth seasons were categorized into four annual quarters (January—March: late rainy season; April-June: early dry season; July-September: late dry season; October—December: early rainy season). Age at first calving was calculated as the period, in days, between the heifer’s birth date and her first calving date (Joaquim et al. 2024).

Criteria for exclusion and inclusion

Animals with incomplete data on AFC, BW, or CI, as well as heifers that had not calved by the time of data collection, were excluded. Specifically, cows with AFC values outside the range of 540 to 1460 days, CI values outside 300 to 730 days, and calves lacking recorded BW or birth date were not considered. In contrast, cows were included if they had complete reproductive records, including an AFC between 540 and 1460 days, an estimated age at first mating (AFM) based on birth and calving dates, and a CI between 300 and 730 days. Calves were included if they had a recorded BW and a known birth date, which allowed for classification by season of birth.

A total of 808 AFM calculated based on recorded birth and calving dates, 305 BW obtained from registration forms and grouped according to the date of birth, and 305 CI calculated as the period, in days, between consecutive birth dates (Joaquim et al. 2024) were included in the analysis.

Statistical analyses

The reproductive performance data of the Angoni cattle were analyzed using R 4.3.2. The Shapiro–Wilk test was applied to evaluate normality for each variable: birth weight of calves (BW), age at first calving (AFC), and calving interval (CI). Results indicated significant deviations from a normal distribution in all traits (BW: W = 0.962, P = 0.002; AFC: W = 0.954, P < 0.001; CI: W = 0.948, P < 0.001). Homogeneity of variances was assessed using Levene’s test, which also revealed significant differences among groups (P < 0.05 for all traits). Given the violation of both normality and homoscedasticity assumptions, nonparametric tests were used. The effects of age at first mating (AFM) and season of dam’s birth (SB) on BW, AFC, and CI were evaluated using the Kruskal–Wallis (Chi-square) test. When significant differences were detected, Dunn’s test was applied for pairwise comparisons between groups. The least squares method was used to assess the relationship between AFM, BW, and AFC through simple linear regression analysis. Prior to regression, linearity, homoscedasticity, and normality of residuals were verified. All analyses were performed at a 5% significance level. Although the dataset covered a 25-year period (1995–2020), year was not included as a fixed factor due to incomplete data and unbalanced sample sizes across years. However, we acknowledge that year effects (e.g., changes in management, climate, or recording accuracy) may act as potential confounders, and this is discussed as a study limitation.

Results

The effects of age at first mating (AFM) and season of dam birth (SB) on birth weights of calves (BW), age at first calving (AFC), and calving interval (CI) are presented in Tables 1 and 2. The analysis considers these parameters to evaluate the impact of AFM and SB.

Table 1.

Effects of age at first mating (AFM) on birth weight of calves (BW), age at first calving (AFC), and calving interval (CI) in Mozambican Angoni cattle raised under tropical conditions.

Age at first mating (Months) BW n Body weight (BW; kg) AFC n Age at first calving (AFC; days) CI n Calving interval (CI; days)
A (<22) 13 17.530 ± 0.765a 13 838.530 ± 2.559a 31 493.480 ± 7.784a
B (22-24.5) 26 17.615 ± 0.623a 26 981.231 ± 3.610b 58 523.845 ± 13.637b
C (24.5-27) 45 17.767 ± 0.293a 45 1059.609 ± 3.571bc 138 520.729 ± 10.099bc
D (27-29.5) 46 18.130 ± 0.358b 46 1139.804 ± 3.025c 133 533.068 ± 9.905b
E (29.5-32) 45 17.578 ± 0.300a 45 1207.913 ± 3.181 cd 111 512.280 ± 11.524bc
F (32-34.5) 40 17.975 ± 0.390ab 40 1287.244 ± 3.566de 91 511.848 ± 11.463bc
G (34.5-37) 56 18.232 ± 0.325b 56 1361.018 ± 2.888e 167 513.821 ± 8.699bc
H (37-39.5) 34 18.324 ± 0.324b 34 1430.750 ± 3.099e 79 508.534 ± 12.212ac
Overall 305 17.916 ± 0.134 305 1203.900 ± 3.141 808 516.010 ± 4.022
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Values are presented as Mean ± S.E.M, with 95% confidence intervals. Different superscripts (a-e) within a column show statistical differences (P < 0.05) among body weights, ages at first calving, and calving intervals, respectively. It should be noted that some statistically significant differences were numerically small and may not indicate strong biological relevance.

Table 2.

Seasonal effects (season of dam birth) on birth weight of calves (BW), age at first calving (AFC), and calving interval (CI) in Mozambican Angoni cattle raised under tropical conditions.

Season of dam birth BW n Body weight (BW; kg) AFC n Age at first calving (AFC; days) CI n Calving interval (CI; days)
1 Late rainy season (Jan-Mar) 86 17.530 ± 0.258a 86 1201.15 ± 17.255a 66 519.640 ± 7.457a
2 Early dry season (Apr-Jun) 40 17.850 ± 0.406a 40 1173.47 ± 21.298a 142 503.130 ± 14.186b
3 Late dry season (Jul-Sept) 55 17.855 ± 0.281a 55 1203.50 ± 19.989a 237 501.560 ± 10.415b
4 Early rainy season (Oct-Dec) 124 18.230 ± 0.191b 124 1215.840 ± 15.400a 363 521.050 ± 5.787a
Overall 305 17.910 ± 0.134 305 1203.920 ± 9.140 808 516.010 ± 4.022
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Values are presented as Mean ± S.E.M, with 95% confidence intervals. Different superscripts (a-b) within a column show statistical differences (P < 0.05) among body weights, ages at first calving, and calving intervals, respectively. It should be noted that some statistically significant differences were numerically small and may not indicate strong biological relevance.

Effects of age at first mating (AFM) on birth weight of calves (BW), age at first calving (AFC), and calving interval (CI)

The analysis of AFM's effect on BW showed that the highest birth weights were recorded in heifers mated at 34.5–37 months (18.230 ± 0.325 kg) and 37–39.5 months (18.324 ± 0.324 kg), while the lowest BW values were observed in heifers mated at less than 22 months (17.530 ± 0.765 kg) and 22–24.5 months (17.615 ± 0.623 kg). Regarding CI, it increased with AFM up to the 27–29.5 month group, where the highest value was recorded (533.068 ± 9.905 days), while the shortest CI (493.48 ± 17.784 days) was found in heifers mated before 22 months. AFM had a significant effect on CI, with the <22-month group differing significantly from the other groups, except for Group G (P < 0.05; Table 1).

Effects of season of dam birth (SB) on birth weight of calves (BW), age at first calving (AFC), and calving interval (CI)

The season of dam birth (SB) had a significant effect on birth weight of calves (BW) (χ2 = 9.31; P = 0.025). Cows born in the last quarter (early rainy season) produced heavier calves (18.23 ± 0.191 kg) compared to those born in the first quarter (late rainy season) (P < 0.05; Table 2). Also, the data for cows born in the last quarter (early rainy season) exhibited higher variability compared to those born in other seasons (Figure 3B). Regarding the age at first calving (AFC), the individuals born in the second season (early dry season) had a lower AFC (1173.475 ± 21.298 days) compared with those born in other seasons. In contrast, those born in the fourth season (early rainy season) had a higher AFC (1215.847 ± 15.400 days) (Table 2). Anyway, the season of dam birth did not significantly influence the AFC in Angoni cattle (χ2 = 2.79; P = 0.42). Concerning the calving interval (CI), the season of dam birth had a significant effect on the CI value (χ2 = 85.60; P = 2.2 × 10−16). Moreover, significant differences in CI value were observed between calvings in the first (late rainy season) and second (early dry season) season (P < 0.05), second (early dry season) and fourth (early rainy season) seasons (P < 0.0001), and third (late dry season) and fourth (early rainy season) season (P < 0.0001). The most prolonged CI value was recorded in calvings occurring in the fourth season (early rainy season) (521.050 ± 5.787 days), while the shortest CI value was observed in calvings occurring in the third season (late dry season) (501.560 ± 10.415 days) (Table 2).

Fig. 3.

Fig. 3.

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Effect of season of dam birth on reproductive and productive traits in angoni cattle. Box-and-whisker plots showing variations in productive and reproductive traits (BW: birth weight of calves; kg, AFC: age at first calving; days, and CI: calving interval; days) and season of dam birth (SB; Jan-Mar: late rainy season, Apr-Jun: early dry season, Jul-Sep: late dry season, Oct-Dec: early rainy season). A) BW vs. SB; B) AFC vs. SB and C) CI vs. SB. Each box encloses the 25th percentile, the line in the middle represents the median and the vertical bars extend to 5th and 95th percentiles of the mean (′×′ symbol) ± SD values. * (P <0.05).

Discussion

This study tested the hypothesis that age at first mating (AFM) and season of dam birth (SB) influence key reproductive traits in Angoni cattle. The results confirmed that AFM significantly affected birth weight (BW), age at first calving (AFC), and calving interval (CI), whereas SB influenced BW and CI but not AFC.

Our findings partly support earlier reports on Bos indicus breeds. The analysis revealed that calves born to dams calving for the first time at younger ages (less than 22 months) exhibited higher birth weights, while the lightest were from those mated before 22 months and at 22–24.5 months. Šlyžienė et al. (2023) emphasized that the effect of dam age on calf BW follows a curvilinear pattern, with very young and older dams deviating from the optimum. Our study observed a similar non-linear relationship between AFM and calf BW. However, unlike Šlyžienė et al. (2023), where heifer management and breeding were controlled, the Angonia Research Station cattle were managed under extensive, year-round mating systems. This difference in production context may explain why the variability was higher in our data, suggesting that management intensification could reduce the negative effects of late mating. This indicates an optimal window where younger dams tend to provide better fetal development due to their good nutritional status and appropriate body condition during gestation. Our findings reinforce the notion that late mating can negatively influence birth weight, a crucial factor for calf viability and early growth performance. These findings contradict those described by Meesters et al (2024) and Van Eetvelde et al (2020) who stated that nulliparous dam age influences fetal development as well, associating both very young and older age with lower birth weights. A curvilinear relationship between dam age and calf birth weight was found by Kamal et al (2014) who suggested that in the very young dams, continued growth of the dam competes with fetal growth. In Figure 2A can be seen that there is no a linear relationship between age at mating and calf’s birth weight which suggests that calf birth weight does not consistently increase or decrease with the dam’s age at mating. This could explain the fluctuations in average birth weight between different mating ages. On the other hand, early mating increases the cow productive lifespan, but it raises concerns about dystocic births. Moreover, the late mating of cows needs to be controlled as it leads to economic losses (Šlyžienė et al. 2023). There is ongoing controversy regarding the impact of mating age on calf growth performance. A study by Stádník et al (2008) found that while calves from cows mated early had significantly higher body weights, they also had significantly lower weight gains. Also, Bitencourt et al. (2020) evaluated the influence of two sub-periods of the calving season, early calving (September 6 to October 15) and late calving (October 16 to November 30) and two stages of maturity (young or adult cows). They found that calves born from adult cows with early calving weighed ∼4.2 kg more than those born from adult cows with late calving. Optimal BW in Angoni cattle appears to be achieved when heifers are bred at 34–39 months.

Fig. 2.

Fig. 2.

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Association between age at first mating and reproductive and productive traits in angoni cattle. Regression analysis of age at first mating (AFM, days) with a) birth weight (BW, kg; n = 305 calves), b) age at first calving (AFC, days; n = 305 heifers), and c) calving interval (CI, days; n = 808 cows) in Mozambican Angoni cattle. Least squares means and S.E.M. (transparent bands) for the interaction between traits: a) Least squares means and S.E.M. for the interaction between birth weight (kg) and age at first mating (days); b) Least squares means and S.E.M. for the interaction between age at first calving (days) and age at first mating (days); c) Least squares means and S.E.M. for the interaction between calving interval (days) and age at first mating (days). P-values of fixed effects: P = 2.2 × 1016; AFC (n = 305 heifers), BW (n = 305 calves), and CI (n = 808 cows) born from 1995 to 2020 at the Angónia Research Station in Mozambique.

Regarding the effect of age at mating on the age at first calving (AFC), a direct and linear relationship was observed between these two indicators. AFC increased directly with AFM, with the shortest AFC observed in heifers mated before 22 months and the longest in those mated at 37–39.5 months. These results confirm that delayed mating correlates with a later onset of first calving (Figure 2B). Heifers introduced to breeding later not only had increased AFC but also highlighted the necessity for timely reproductive practices. This direct relationship is evident in A group, which had the lowest AFC value (Table 1). This is critical considering that prolonged AFC impairs reproductive efficiency, leading to higher management costs and resource use (Burns et al. 2010; Turiello et al. 2020). This linear relationship between AFM and AFC is consistent with Perry (2016) and Larson et al. (2016), who noted that delayed mating results in proportionally delayed calving. Nutritional status prior to breeding has been highlighted by Sammad et al. (2022) and Mourão (2020) as critical for achieving reproductive maturity, with faster-growing heifers reaching AFC earlier. The absence of SB influence on AFC in our study is in line with Earnhardt et al. (2021), who found that AFC is more strongly associated with genetic and management factors than with birth season. This pattern aligns with reports from Nelore cattle in Brazil, where later breeding was associated with extended AFC and economic losses (Perry 2016; Turiello et al. 2020). Similarly, Indian zebu breeds such as Gir and Sahiwal show delayed reproductive maturity and long calving intervals under extensive management (López-Paredes et al. 2018). In West African Fulani cattle, delayed puberty and long AFC are also reported as productivity bottlenecks (Maule 1973; Ng’Ang et al. 2018). These findings suggest that earlier mating leads to earlier AFC, offering potential gains in lifetime productivity, provided heifers reach adequate body condition before breeding.

Calving interval (CI) was influenced by AFM. The shortest CI occurred in heifers mated before 22 months (493.48 ± 7.78 days). Our study showed that heifers calved at approximately 24-31 months, which is desirable for maximizing reproductive efficiency. In this study, CI was shown to be linked to the reproductive and productive longevity of cows, a crucial characteristic for establishing successful beef cattle breeding programs. The CI, among other reproductive indicators, is one of the primary reasons for cow culling, as it hinders the achievement of the reproductive and productive objectives of the unit (Summers et al. 2018). Heifers that were mated by 22 months had shorter CI values. The association between earlier breeding and shorter CI is supported by Mourão (2020) and Wichman et al. (2022), who emphasized the role of pre-breeding weight targets in improving conception rates and reducing CI. Since the Angonia Research Station (ARS) did not implement specific supplementation for heifers before the breeding season, this might be a reason only a few heifers succeeded in the first breeding season before 22 months. Mourão (2020) and Wichman et al. (2022) emphasize that heifers should attain 70–75% of their adult weight thirty to forty-five days before entering the breeding season. This weight gain allows heifers to complete two to three estrus cycles before the introduction of bulls, thereby increasing the likelihood of conception early in the breeding season (Mourão 2020). Implementing targeted nutritional strategies and focusing on early reproductive traits can contribute significantly to the sustainability and efficiency of the production system (Mourão 2020). Overall, the linear regression could not explain direct or linear relationship between age at mating and calving interval.

Regarding season of dam birth and birth weight of calves (BW), calves from dams born in the early rainy season had higher BW than those from dams born in the late rainy season. The seasonal BW of Angoni calves in this study align with the findings of (Joaquim et al. 2024), who reported an average birth weight of 18.49 kg in their research based on the generation interval and calving season’s impact on the main reproductive and productive parameters in Angoni cattle. The season of dam birth significantly affected calf BW, with calves from late rainy season births showing lighter weights compared to those born in early rainy season. This discrepancy may be attributed to environmental factors such as pasture quality and maternal nutritional status during the critical prenatal period (Tuska et al. 2022). According to Maciel et al. (2016), in Mozambique, the breeding season is divided into two phases: the mating season from January to April (late rainy season) and the calving season from October to December (early rainy season). This division is because of the seasonality of native pasture, which is crucial for cattle production. Consequently, reproductive activities follow this pattern, with mating occurring at the end of the rainy season when cows are in good body condition, exhibit prolonged estrus, and are more fertile. Calving, therefore, occurs at the beginning of the rainy season, facilitating the birth of heavier calves. This phenomenon could be attributed to the increase in placental blood flow during this seasonal period, which redirects approximately 30% of the dam’s nutrient supply to support fetal growth (Vonnahme et al. 2018). Also, favorable ambient temperatures during this seasonal period ensure an adequate nutrient supply for optimal intrauterine fetal development (Tuska et al. 2022). This period coincides with Mozambique’s rainy season, providing favorable conditions for dams to achieve a good body condition score, resulting in the birth of heavier and more viable calves (Joaquim et al. 2024; Maciel et al. 2016). However, except for the last season, the birth weights of calves from cows born during the other birth seasons considered in this study were not significantly different from each other (Figure 3A). Similar results were observed in studies by (Barroso et al. 2023), who investigated the effects of birth season on birth weight in Hanwoo cattle, a local breed native from Korea, and found no significant differences in the birth weights of calves born in spring, autumn, and winter. Another study in Brazil reported that the average birth weight of calves did not vary significantly between seasons (Rezende et al. 2020). Finally, Wichman et al. (2022) suggested that birth weights depend on factors such as geographic location, management practices, the specific timing of birth, and other variables that may restrict intrauterine growth. Nonetheless, when evaluating the effect of the time of birth of the dams concerning the birth weight of their calves, it was found that dams born in the first quarter of the year (late rainy season) produced less heavy calves. Here, the season of dams′ birth had a significant effect on the birth weight of their offspring. Optimal BW in Angoni cattle appears to be achieved when dams are born in seasons that align gestation with periods of high forage quality.

Regarding the season of dam birth (SB) and the age at first calving (AFC), the SB did not significantly influence AFC. The results obtained in the present study align with those described by Joaquim et al. (2024) for Angoni cattle from Malawi and Mozambique. The second season (early dry season) had the lowest AFC, whereas the last season (early rainy season) had the highest. However, the birth season had no significant influence on the AFC of Angoni cows in the present study (Figure 3B). These results are consistent with those obtained by Earnhardt et al. (2021), who evaluated the influence of the calving group, time of birth, and year of birth on the age at first calving and calving groups in Brahman heifers. According to these authors, many factors can affect the age at first calving in heifers, such as the dam, sire, season of birth, year of birth, nutrition, antral follicle count, and health (Earnhardt et al. 2021).

Calving Interval was influenced by season of dam birth. The shortest CI occurred in dams born in the late dry season during July to September in Mozambique, while the longest CI was observed in dams born in the early rainy season. These results confirm that the dams′ birth season significantly affects reproductive life and, consequently, the average productivity of cows throughout their lifespan (Figure 3C), which aligns with the availability of high-quality forage during this time, supporting effective lactation and recovery post-calving due to cows’ natural adaptation to environmental changes to meet their nutritional needs, both for breastfeeding the calf and for recovering their energy reserves and body condition to enter mating again after the puerperium. Seasonal variation in CI in our study agrees with Fernandez-Novo et al. (2020) and Harvey-Sky et al. (2024), who reported that environmental conditions, forage availability, and metabolic adaptations after calving directly influence the time to rebreeding.

In Mozambique, shortly after the natural calving season, high-quality forage is more readily available, requiring little or no supplementation. This leads to better milk production, allowing calves to grow and develop more effectively, which increases their potential productivity and shortens the CI. Conversely, calves born outside the natural season, when forage resources are more limited, face greater demands in terms of food and health management, leading to lower productivity and longer CIs (Harvey-Sky et al. 2024). Also, there is evidence that the calving season can influence gestation length, which might contribute to the shorter CI observed in cows calving during the natural season. Moreover, Fernandez-Novo et al. (2020) have reported seasonal differences in the number and size of follicles in beef cattle, changes in serum progesterone concentrations, and variations in estrous cycle durations, all of which affect reproductive performance. Overall, SB had a recognized influence on CI, being shorter when calving coincides with seasons of high forage quality, which supports faster postpartum recovery and earlier return to oestrus. It is also important to recognize that the data span over two decades (1995–2020), during which changes in management practices, climatic variation, and disease control strategies may have influenced reproductive outcomes. Because of data imbalance across years, these temporal effects could not be statistically controlled in the present analyses. Therefore, year remains a potential confounding factor and should be carefully considered in future studies with more balanced datasets.

Conclusion

This study demonstrates that age at first mating significantly influences both reproductive and productive traits in Angoni cattle under tropical conditions. Additionally, the season of dam birth was associated with variation in calving intervals and birth weights of calves, suggesting a potential long-term influence of early-life environmental conditions on reproductive performance. These findings contribute to a better understanding of how early reproductive traits and seasonal factors affect productivity in indigenous cattle. They may also inform the development of breeding strategies tailored to the specific challenges of tropical production systems. For ranchers, aligning breeding seasons so that late gestation and early lactation coincide with periods of abundant forage can help improve calf BW and shorten CI. For practical application, we recommend initiating breeding in Angoni heifers between 27 and 29.5 months of age, as this range balances calf birth weight and calving interval without compromising animal health. Furthermore, mating plans should consider the dam’s birth season, with preference for heifers born in the dry season, as these animals are more likely to exhibit shorter subsequent calving intervals. Further studies should integrate molecular tools to confirm breed-specific genetic markers, evaluate the interaction between nutrition and reproductive performance under different seasonal conditions, and assess the long-term economic benefits of optimized breeding calendars for indigenous cattle production systems in Mozambique.

Limitation of the study

Although the present study provides novel insights, its retrospective and unbalanced dataset limited the use of more robust statistical models. Specifically, generalized linear mixed models (GLMM), which are more suitable for hierarchical and longitudinal data, could not be applied. We acknowledge this as a limitation and recommend that future studies with more balanced datasets adopt GLMMs to better capture random effects (e.g., year, group, or individual variability) and to strengthen causal inference.

A further limitation is that AFM was estimated using a fixed gestation length of 280 days. Although this is a common approximation in retrospective cattle studies, gestation length can vary depending on breed, calf sex, nutrition, and environment. This assumption may introduce some imprecision at the individual level, but the large sample size and use of group-level analyses likely reduced its influence on overall results. Future studies with direct mating records or flexible gestation estimates would strengthen accuracy. It should also be noted that intra-group variability was relatively high in groups with small sample sizes, leading to large standard errors. This reflects both biological variation and the retrospective, unbalanced nature of the dataset. Consequently, estimates for these groups should be interpreted with caution, and future research should prioritize larger and more balanced datasets to improve precision. Although statistically significant differences were detected across several groups, some of these differences were numerically minimal (e.g., <0.5 kg in BW; <10 days in CI), suggesting limited biological relevance. In addition, intra-group variability was high in categories with small sample sizes (e.g., n = 13), leading to relatively large standard errors.

Acknowledgement

The authors are grateful for the support provided by the Agricultural Research Institute of Mozambique—Angonia Research Station for providing the data.

Contributor Information

Abilio Paulo Changule, Center for Genetic Resources and Animal Assisted Techniques (CRGTRA), Directorate of Animal Science (DCA), Agricultural Research Institute of Mozambique (IIAM), Matola 1410, Mozambique.

Leonel António Joaquim, Institute of Veterinary Medicine Federal University of Para (UFPA), Castanhal 68740-000, Brazil.

Milton Paulo Morrombe, Graduate School of Integrated Science for life, Faculty of Veterinary Medicine, Hiroshima University, Higashi-Hiroshima City, Hiroshima 739-8528, Japan.

Hermenegilda Petersburgo Dias, Faculty of Agricultural Science, Licungo University (UniLicungo), Quelimane 2400, Mozambique.

Tiago Pereira Guimarães, Instituto Federal Goiano, Campus Rio Verde 75901-970, Brazil.

Manuel Garcia-Herreros, National Institute for Agricultural and Veterinary Research (INIAV), Santarém 2005-424, Portugal; CIISA-AL4AnimalS, Faculty of Veterinary Medicine, University of Lisbon, Lisbon 1300-477, Portugal.

Custódio Gabriel Bila, Department of Animal and Public Health, Faculty of Veterinary Medicine, Eduardo Mondlane University (UEM), Maputo 1304, Mozambique; Department of Research and Development, Intermed Mozambique Lda, Maputo 1304, Mozambique; Center of Excelence in Agri-Food Systems and Nutrition (CEAFSN) - Eduardo Mondlane University (UEM), Maputo 257, Mozambique; Faculty of Veterinary Medicine and Animal Science, Save University (UniSave), Gaza Delegation, Chongoene 1206, Mozambique.

Funding

This research was supported by Intermed Mozambique, Lda (Grant number [IMR521/24]). Author Custódio Bila has received research support from Company Intermed Mozambique, Lda.

Author contributions

Abilio Paulo Changule, Leonel António Joaquim and Milton Paulo Morrombe contributed to the investigation, methodology, analyses, and original draft writing. Mariana Novela, Florentina Domingos Chilala and Hermenegilda Petersburgo played roles in reviewing, editing, interpreting, and discussing the results. Tiago Guimarães, Manuel Garcia Herreros and Custódio Gabriel Bila: Project administration, Resources, Supervision, Validation, Writing review and editing. All authors have thoroughly read and approved the final manuscript.

Conflict of interest: The authors certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.

Data availability

The authors declare that no additional data were used to generate the paper’s results.

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Data Availability Statement

The authors declare that no additional data were used to generate the paper’s results.

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